At least 14 people - most of them women - were killed by gunmen in a nightclub in the northern Brazilian city of Fortaleza, a local newspaper reported, citing police.

A number of armed men stormed the venue early Saturday and started shooting, Diario do Nordeste reported, adding that six other people, including a 12-year-old boy, had been injured.

Police said they were working on the assumption that the incident was part of an ongoing battle between two rival drug gangs named Guardioes do Estado (Guardians of the State) and Comando Vermelho (Red Commando).

In Ceare, the state in which Forraleza is located, some 5,000 killings were reported last year, marking a 50-percent increase on 2016. The majority were drug-related.